1. Field of the Invention
The present invention relates to an automatic holographic display device, and more particularly, to an automatic holographic display device that can display 3-dimensional holographic images using a parallax barrier method by using a modulated cholesteric liquid crystal panel and a phase difference plate, wherein liquid crystal in the modulated cholesteric liquid crystal panel is directly driven by an electrode, thereby electrically enabling mutual conversion between two-dimensional flat images and three-dimensional holographic images, and improving transmittance of three-dimensional holographic images when displayed.
2. Description of the Related Art
In general, 3-dimensional holographic images can be displayed by separating left eye images and right eye images to have binocular disparity.
Therefore, users generally wear specific spectacles having different polarization components for the left and right eyes, and thus can view holographic images displayed in image display devices. However, users have to wear separate specific spectacles in order to view holographic images.
To overcome such inconvenience, image display devices in which left eye images and right eye images are directly separated, and thus users can view holographic images without wearing specific spectacles have been recently developed. In addition, automatic holographic display devices in which an intermediate via a switching element that separates left eye images and right eye images is formed, if desired, and thus 2D flat images can be viewed as is most often the case, and can be converted to 3D holographic images, if necessary have been developed.
In general, automatic holographic display devices display 3D holographic images by using a parallax barrier. A parallax barrier allows a display device to show three-dimensional images such that vertical or horizontal slits are formed in front of images corresponding to the left and right eyes, and holographic images synthesized through the slits are separated and observed.
Herein, automatic holographic display devices can be classified into front barrier type devices and rear barrier type devices depending on whether the parallax barrier is positioned in front of or behind an image panel that displays images.
FIG. 1 is a cross-sectional view of a conventional holographic display device. Referring to FIG. 1, the conventional holographic display device includes an image panel 200 and polarizers 100. The image panel 200 includes a color filter 220, an image liquid crystal layer 230 and a conventional thin film transistor (not shown) between an upper substrate 210 and a lower substrate 240, and displays images by an operation of the thin film transistor. The polarizers 100 are respectively disposed above and below the image panel 200.
A barrier panel 300 in which slits are formed through a parallax barrier 310 is disposed below the polarizer 100 disposed below the image panel 200, and another polarizer 100 is disposed below the barrier panel 300.
Reference numeral 330 denotes transparent plates that are respectively formed above and below the parallax barrier 310.
Herein, an aperture ratio of the barrier panel 300 directly affects transmittance when 3-dimensional images are viewed. In general, to display natural 3D images, the parallax barrier 310 should account for a large portion of the barrier panel.
In a liquid crystal display device using the barrier panel 300, the parallax barrier 310 is designed to have an aperture ratio of 40% or less. For example, if a 2D flat image has a luminance of 500 cd (candela) per unit area when viewed, a 3D holographic image has a maximum luminance of m 200 cd (candela) per unit area when viewed. Thus, the optical efficiency is largely decreased.
To address these problems, Korean Patent Application No. 10-2002-0085356 discloses a holographic display device. In this holographic display device, cholesteric liquid crystal layers are disposed to be separated from each other, and a liquid crystal panel is separately disposed between the cholesteric liquid crystal layers. A switching operation of the liquid crystal panel can enable mutual conversion between 2D flat images and 3D holographic images. In addition, a phase difference plate and a polarizer are disposed above the upper cholesteric liquid crystal layer.
However, the holographic display device disclosed in the aforementioned application has problems such that the liquid crystal panel has to be separately designed for mutual conversion between 2D flat images and 3D holographic images, multiple layers are adhered in the manufacturing process, thereby complicating the manufacturing process, optical transmittance is decreased, and luminance is reduced.